1. Field of the Invention
This invention relates to adhesives. More particularly, this invention relates to polymerizable adhesives useful in dental applications, and to processes for using such dental adhesives. The adhesives of the present invention and the methods of using them find particular utility in bonding crowns, veneers, caps, bridges, repairs and other prostheses to tooth structures. The dental adhesive systems of the invention comprise polymerizable compositions and methods of use in which the compositions may be polymerized by visible light. Such compositions are suitable for through-the-tooth curing so that prosthetic devices may effectively be adhered to tooth structure. Additionally, such adhesives find use in endodontics, orthodontics and other specialized dental and oral applications.
Adhesive compositions useful as dental cements are primarily evaluated by their physical and chemical characteristics. Some of the more important properties include coefficient of thermal expansion, tensile strength, compressive strength, and film thickness required for effective adhesion. Other factors include toxicity, ease of working, and leachability.
It is desirable to select a dental cement having a coefficient of thermal expansion which closely matches the coefficient of thermal expansion of teeth. If the coefficient of thermal expansion of a dental cement is not closely matched to that of the tooth to which it is applied, the normal expansion and contraction of the cement and tooth caused by temperature variations (such as by exposure to hot and cold food and beverage) may cause a cemented prosthesis to detach from the tooth. It is also advantageous to maximize the tensile and compressive strengths of the dental adhesive since the forces to which the tooth and repair structures are exposed during chewing, grinding, or tearing may be quite severe.
It is also desirable to minimize the film thicknesses of adhesive coating materials used in dental applications. Thinner films may effect closer contact between the surfaces to be joined, are less susceptible to erosion by leaching, and are more efficiently cured by visible light polymerization systems. It is also desirable for dental cements to demonstrate toxic acceptability, ease in handling, and minimal leaching.
2. Description of the Prior Art
A variety of organic and inorganic materials have been used as dental cements. Some of the more common ones include: glass ionomer cements such as those which contain aluminosilicopolyacrylic acids, zinc oxyphosphate systems, polycarboxylate cements, and zinc oxide and eugenol mixed with particles of a polymer such as methylmethacrylate. Both chemical and/or mechanical bonding may be involved in such adhesive systems.
Numerous organic materials with or without filler materials have been tried as dental adhesives. U.S. Pat. No. 3,709,866 to Waller, assigned to the assignee of this invention, discloses a two-part photopolymerizable dental composition useful as a dental cement which comprises a monomeric liquid and a catalyst liquid. The monomeric liquid may comprise the hexamethylene diisocyanate adduct of bis-GMA. As used herein the term "bis-GMA" means 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane, also referred to as "diglycidyl methacrylate of bisphenol A". As used herein the term "bisphenol A" means 2,2-bis(4-hydroxyphenyl)propane. The catalyst liquid of the two component system of Waller contains an ultraviolet light sensitive material such as benzoin methyl ether. Use of bis-GMA in dental filling materials and restoratives is described in U.S. Pat. No. 3,539,333 to Lee et al and U.S. Pat. No. 4,097,994 to Reaville et al.
U.S. Pat. No. 3,835,090 to Gander et al teaches a dental restorative cement comprising a trimethacrylate or triacrylate monomer ester of an aliphatic triol together with bis-GMA and an inorganic filler material in a peroxide-catalyzed system.
U.S. Pat. No. 3,660,343 issued to Saffir, and assigned to the same assignee as this application, discloses a thermosetting epoxy resin hardened with an N-3-oxohydrocarbon substituted acrylamide which may be useful as a dental cement when the addition of filler is no more than 40% based upon the total weight of the composition.
U.S. Pat. No. 4,089,763 to Dart et al teaches a method of repairing teeth using isocyanate modified bisphenol A derivatives and a reducing amine in conjunction with a visible light cured system. Camphoroquinone is described as being the preferred photosensitive component.
European Patent Application No. 0012535 in favor of I.C.I. Ltd. discloses dental compositions comprising a vinyl urethane prepolymer and processes for their manufacture. Substituted norbornane diones are included as photosensitive catalysts.
U.S. Pat. No. 3,677,920 to Kai et al discloses photopolymerizable diisocyanate modified unsaturated polyesters containing acrylic monomers.
U.S. Pat. No. 4,222,835 to Dixon teaches a composition prepared of a liquid vinyl monomer, a UV-activated photoinitiator, a thermal initiator, and an accelerator.
U.S. Pat. No. 4,228,062 to Lee, Jr. et al discloses a rapid setting adhesive of low toxicity having high bond strength to a variety of metals and plastics, and particularly to stainless steel, polycarbonate plastics and tooth enamel. Glycidyl methacrylate is taught as a preferred resin. Conventional peroxide polymerization catalysts are used along with conventional polymerization inhibitors.
Previous dental cements such as those disclosed above have exhibited tensile strengths in the range of 5-20 meganewtons/m.sup.2 (Mn/m.sup.2), and compressive strengths less than about 200 Mn/m.sup.2. Applications of such dental cements have resulted in adhesive layer thicknesses of about 25 microns.